in the assembly of electronic components, typified by, but not limited to vacuum tubes, a common step is the sealing of a glass or metalized ceramic "tube" or enclosure to a metal or metalized ceramic base. The sealing or brazing operation is typically accomplished in a high temperature furnace with the components to be joined being held in position by a fixture. A primary requirement of the fixturing material is that the brazing compound or insulative material used to join the two components must not adhere to the fixture.
In the past, suitable fixtures were fabricated from graphite and stainless steel with the choice of material being dependent upon the atmosphere used in the high temperature furnace. Stainless steel fixtures are most commonly used in a furnace atmosphere of hydrogen containing trace amounts of moisture. Moisture reacts to form a passive oxide coating on the stainless steel surface to which the brazing compound or insulative material will not adhere. However, when brazing under vacuum or in a dry hydrogen atmosphere the oxide layer does not form and the brazing compound or joining material tends to adhere to the stainless steel fixture thus making it difficult if not impossible to remove the assembled electronic component.
While most brazing compounds do not readily adhere to graphite fixtures, use of such fixtures in the electronics industry has not been accepted because the material readily generates particulates which can contaminate the components to be joined and/or the joining material. Moreover, residual oxygen within the furnace atmosphere causes rapid degradation of graphite and reduces the useful lifetime of the fixture.
Many uses have been found for composite coated articles. For example, U.S. Pat. No. 3,874,900, assigned to Materials Technology Corporation, a subsidiary of Air Products and Chemicals, Inc., discloses heated substrates coated by successive vapor deposition of titanium carbide and titanium nitride. These multi-layer composites serve as coatings for metal and composite metal parts such as tools, dies and the like and are designed to reduce wear of the work surfaces.
U.S. Pat. No. 4,565,747 teaches vapor deposition of boron nitride containing from about 0.05 to 10 wt % titanium nitride. Example 7 teaches the preparation of a triple-layer composite ceramic body wherein graphite is coated with boron nitride containing titanium nitride. These composites are employed as heat resistant materials in high temperature service or as materials for use in manufacturing metallic or semiconductor articles.